1. Field of the Invention
The present invention relates to a novel cyclic sulfide compound, polymerizable compositions comprising it for manufacturing optical products and optical products obtained therefrom.
2. Description of the Prior Art
Plastic lenses, as compared with glass lenses, have various advantages such as light in weight, hard to crack, easy to mold and ready to dye and so on. These characteristic features being appreciated, they have recently established an important position as optical materials.
Heretofore, what is generally used as resins for lenses of eyeglass, prisms or optical fibers etc. are poly(methyl methacrylate), polycarbonate, poly(diethylene glycol bisallylcarbonate) etc. Particularly, as lens materials for glasses, poly(diethylene glycol bisallylcarbonate) has most frequently been used because of its excellent transparency, processability, surface hardness and so on.
But because of its low refractive index (n.sub.D =1.50), lenses made from it for the correction of acute myopia or hypermetropia should be thick and heavy, thus raising problems that a plastic lens' advantage of being light in weight is lost and also aesthetic appearance is greatly impaired. For improving the above drawbacks, some lens materials having higher refractive indices have been proposed. Examples of compounds having refractive indices of 1.60 or higher abound, especially among compounds containing sulfur atoms (e.g. Japanese Patent Laid-Open Publication Sho 59-87126, U.S. Pat. Nos. 4,689,387 and 4,780,522, Japanese Patent Laid-Open Publication Sho 63-150324 and 63-199210, Hei 1-163701 and 1-242612, U.S. Pat. No. 5,087,758 and E.P. No. 435306).
On the other hand, the market of plastic lenses has developed along the course of nearly stepwise advances by 0.05 in the refractive index, namely from the low index of 1.50 through the middle index of 1.55-1.56 and the high index of 1.60-1.61 to the superhigh index of 1.65 or above, so that lens materials of the intermediate refractive indices (e.g. 1.58) are not much demanded. Optical products obtained by using the novel cyclic sulfide compound of this invention are those classified as products which have high or superhigh refractive indices. An important factor to be considered with materials of high refractive indices is the Abbe number, which is the index of chromatic dispersion. Generally, plastic lenses tend to have lower Abbe numbers with increasing refractive indices. Thus the chromatic dispersion becomes larger, tending to produce a rainbow at the rim of each lens, and this causes greater fatigue of the eyes. Accordingly, it is important to balance the refractive index with the Abbe number in developing commercially useful lens materials. Thus lens materials having high refractive indices and adequately high Abbe numbers are sought. Besides the refractive index and the Abbe number, important physical properties that are demanded of plastic lenses are e.g. low sp.gr. for obtaining lighter products, high thermal resistance not to be deformed by the heat of dyeing or grinding, high impact resistance to be less crackable and for assurance of higher safety, and high light resistance to avoid yellowing by ultraviolet ray etc. Balances between all of these physical properties is of importance. Lens materials hitherto proposed including those of the aforementioned prior art involved problems such that when they were designed to have higher refractive indices, 1.60 or higher, they tended to give lower Abbe numbers, increase in the sp.gr. or manifested degradation in their thermal, impact and light resistance or dyeability.
The compound disclosed in E.P. No. 435306, having an alicyclic structure with sulfide bonds, gives the lens with refractive index of the superhigh class and relatively high Abbe number. However, its addition polymerization with alicyclic polyisocyanates yielded lenses with refractive indices of 1.62 which does not meet the market's demand. Further blending with such an aliphatic polythiol as pentaerythritol tetrakis(mercaptoacetate) made it possible to adjust the refractive index to 1.60 (with the Abbe number of 40), but deterioration of the thermal resistance was notable.